Body Mass Index and Pneumothorax Risk After CT-Guided Pulmonary Nodule Localization: A Nonlinear Analysis Using Restricted Cubic Splines

Objective: Pneumothorax remains the most frequent complication of CT-guided pulmonary nodule localization, yet the role of body mass index (BMI) is poorly understood. We investigated the nonlinear relationship between BMI and pneumothorax risk using restricted cubic spline (RCS) analysis. Methods: In this retrospective cohort study, 175 patients undergoing CT-guided localization for solitary pulmonary nodules (≤20 mm) were analyzed. Multivariable logistic regression and RCS models adjusted for clinical/procedural confounders identified BMI threshold effects. Results: The overall pneumothorax rate was 34.3% (60/175). RCS revealed a nonlinear relationship (P for nonlinear=0.015), with an inflection point at BMI=24.7 kg/m². Below this threshold, each 1-unit BMI increase reduced pneumothorax risk (OR: 0.65, 95% CI: 0.52–0.82; P<0.001), while no significant association was observed above it (OR: 1.40, 95% CI: 0.97–2.03; P=0.073). Conclusion: BMI exhibits a U-shaped association with pneumothorax risk, with optimal protection at BMI=24.7 kg/m². Thin patients (BMI<24.7 kg/m²) may benefit from refined techniques (e.g., thinner needles, coaxial approach) to mitigate risk. Keywords: Pulmonary nodule; CT-guided localization; Pneumothorax; Obesity paradox; Threshold effect